Coexpression of ligand-gated P2X and G protein-coupled P2Y receptors in smooth muscle. Preferential activation of P2Y receptors coupled to phospholipase C (PLC)-beta1 via Galphaq/11 and to PLC-beta3 via Gbetagammai3.
P2 receptor subtypes and their signaling mechanisms were characterized in dispersed smooth muscle cells. UTP and ATP stimulated inositol 1,4,5-triphosphate formation, Ca2+ release, and contraction that were abolished by U-73122 and guanosine 5'-O-(3-thio)diphosphate, and partly inhibited (50-60%) by pertussis toxin (PTX). ATP analogs (adenosine 5'-(alpha, beta-methylene)triphosphate, adenosine 5'-(beta, gamma-methylene)triphosphate, and 2-methylthio-ATP) stimulated Ca2+ influx and contraction that were abolished by nifedipine and in Ca2+-free medium. Micromolar concentrations of ATP stimulated both Ca2+ influx and Ca2+ release. ATP and UTP activated Gq/11 and Gi3 in gastric and aortic smooth muscle and heart membranes, Gq/11 and Gi1 and/or Gi2 in liver membranes, and Go and Gi1-3 in brain membranes. Phosphoinositide hydrolysis stimulated by ATP and UTP was mediated concurrently by Galphaq/11-dependent activation of phospholipase (PL) C-beta1 and Gbetagammai3-dependent activation of PLC-beta3. Phosphoinositide hydrolysis was partially inhibited by PTX or by antibodies to Galphaq/11, Gbeta, PLC-beta1, or PLC-beta3, and completely inhibited by the following combinations (PLC-beta1 and PLC-beta3 antibodies; Galphaq/11 and Gbeta antibodies; PLC-beta1 and Gbeta antibodies; PTX with either PLC-beta1 or Galphaq/11 antibody). The pattern of responses implied that P2Y2 receptors in visceral, and probably vascular, smooth muscle are coupled to PLC-beta1 via Galphaq/11 and to PLC-beta3 via Gbetagammai3. These receptors co-exist with ligand-gated P2X1 receptors activated by ATP analogs and high levels of ATP.
Murthy
K S
KS
Departments of Medicine and Physiology, Medical College of Virginia, Richmond, Virginia 23298-0711, USA.
Makhlouf
G M
GM
D000249:Adenosine Monophosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism* / Q000502:physiology; D054799:Phospholipase C beta; D058910:Purinergic P2 Receptor Agonists; D011817:Rabbits; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000494:pharmacology
D007527:Isoenzymes; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D019204:GTP-Binding Proteins; D002118:Calcium; D014544:Uridine Triphosphate